One thing I've noticed with Japan is that over the years certain flavors cycle repeatedly in popularity- chestnut (kuri), plum (ume), purple sweet potato (beni imo), and green tea (matcha). You can find the flavors in all kinds of things from ice cream, Kit Kats, Pringles, even Coca-Cola. The flavor trend has also been creeping over to the US the past few years and the green tea flavor in sweets and drinks seems to be a favorite among many people I know. I was at the grocery store yesterday and caught sight of these green tea products (among others) lining the shelves: